Identification and quantification of the sea spray effect on isotopic systems in α-cellulose (δ13C, δ18O), total sulfur (δ34S), and 87Sr/86Sr of European beach grass (Ammophila arenaria, L.) in a greenhouse experiment

The sea spray effect can severely influence the isotopic signature of terrestrial individuals in coastal regions. To further specify this effect, beach grass was grown in a greenhouse under controlled environmental conditions and sprayed with mineral salt solution containing different mineral salts but only traces of NaCl (group 1). Another group of plants was sprayed with salty water from the Schlei inlet and the Baltic Sea, respectively (group 2). Control plants were only sprayed with tap water. Isotope analyses were conducted on the unwashed and washed plants (δ¹³Ccₑₗₗᵤₗₒₛₑ, δ¹⁸Ocₑₗₗᵤₗₒₛₑ, δ³⁴Sₜₒₜₐₗ S, ⁸⁷Sr/⁸⁶Sr), soil (δ¹⁸Oₛᵤₗfₐₜₑ, δ³⁴Sₛᵤₗfₐₜₑ, ⁸⁷Sr/⁸⁶Sr), and spray as well as irrigation water (δ¹⁸Oₛᵤₗfₐₜₑ, δ³⁴Sₛᵤₗfₐₜₑ, ⁸⁷Sr/⁸⁶Sr). Moreover, elemental analyses were performed on the water samples. The sea spray effect was visible in all isotopic systems under study. The uptake of SO₄²⁻, HCO₃⁻, and Sr²⁺ directly affected plants of group 1, while plants of group 2, sprayed with salty water, additionally showed salinity stress in the case of α-cellulose and total sulfur due to biochemical reactions of the plants. Very high concentrations in HCO₃⁻ or SO₄²⁻ also affected the plants' isotopic signatures. The impact of the sea spray and additional stress reactions were quantified. Our study is the first experiment creating an artificial sea spray effect in a greenhouse. This experiment for the first time enables the identification and quantification of the sea spray effect in environmental samples. The marine signature taken up by the plants and recorded by the investigated isotopic systems is apparently high and should have an impact on the isotopic fingerprints of animal consumers at the coast, as evidenced for archaeological animals from the Viking Haithabu and the early medieval Schleswig sites located close to the Baltic Sea. This result demonstrates the potential of greenhouse experiments as an isotopic predictor of the past local sea spray effect.